Who selects for the library collection?

Librarians' specialist knowledge and skills in collection management should be combined with users and people with subject expertise. It is essential a selection policy is written that outlines roles and responsibilities. If the selection policy is written with a clearly outlined decision making model included, there shouldnt be any issues with who selects what. Sometimes it will be the librarian and sometimes it will be a student or a teacher that identifies and requests a new resource. As long as it meets the criteria and budget, it is the policy that makes the final decision. What do others think?